Olefin polymers, such as polyethylene and polypropylene, can be produced in a closed loop reactor that is generally defined by a conduit in the form of a closed loop. The olefin polymers are typically produced by circulating a monomer, a catalyst, and a diluent in the closed loop reactor, which produces a slurry of particulate polymer solids suspended in a liquid medium, such as the reaction diluent, along with unreacted monomer, comonomer, and catalyst. Examples of such polymerization processes are described in U.S. Pat. Nos. 6,239,235; 5,455,314; 5,565,175; WO 01/05842; 6,420,497; 4,613,484; 6,281,300; 2,825,721; 3,152,872; and 3,293,000, the disclosures of which are incorporated herein by reference in their entireties.
In polyethylene processes, isobutane is typically used as the diluent. In polypropylene processes, typically no external diluent is added, but polymer solids are suspended in unreacted propylene, which performs a similar function in polypropylene processes as the diluent performs in typical polyethylene processes. Components, such as hexane, pentane, propane, or other similar compounds can also be included in the diluent. Unreacted monomer and comonomers can include compounds such as ethylene, propylene, butene, hexene, decene, and the like. The polymer solids are suspended within the diluent and are removed from the slurry loop reactor as a reactor product within a discharge slurry. However, because the polymer solids are suspended within the discharge slurry, diluent is also typically removed from the reactor within the discharge slurry, along with the polymer solids. The polymer solids and the diluent then need to be separated through a series of processing steps downstream of the reactor, with the diluent typically being recycled back to the slurry loop reactor.
The downstream processing of the diluent contributes to the overall cost of the polyolefin production process. Consequently, it is cost-beneficial to minimize the amount of diluent that must be processed downstream of and recycled back to the reactor. To decrease the amount of such diluent, it is desirable to increase the concentration of polymer solids in the discharge slurry being discharged from the reactor without plugging or causing other problems during operation of the slurry loop reactor.